What is the probability that a 3rd degree burned hand that has received a skin graft will look normal?

No. "third degree" burn is injury to all tissue from skin into the fatty/subcutaneous layer. That is why the burned tissue was removed and replaced with a graft. Grafts may look very good - depending on size, location, patient conditions, etc. - but the doctor cannot make a graft look the same as unijured skin.
Not great. There are ways to try to make the grafted area look better. A non-meshed or sheet graft tends to be look better than a meshed graft. Generally, skin grafted areas never quite look "normal".